Wheel loader

ABSTRACT

Provided is a wheel loader having an HST type driving system. In order to make it possible to improve working efficiency in an eco mode when a power mode and the eco mode have been set in the wheel loader, the wheel loader is provided with a controller  18  which has an eco mode characteristic line  31,  a power mode characteristic line  32,  and a lifting operation characteristic line  34  having a matching point C located between a matching point A between a working device operating engine torque characteristic line  30  and the eco mode characteristic line  31  and a matching point B between the working device operating engine torque characteristic line  30  and the power mode characteristic line  32.  The controller  18  includes a control portion which controls an HST pump  11  in accordance with the lifting operation characteristic line  34  when lifting operation of a lift arm  4  is detected in the condition that the eco mode has been selected by a work mode selecting portion  22.

TECHNICAL FIELD

The present invention relates to a wheel loader having an HST typedriving system.

BACKGROUND ART

As this type of wheel loader, there is a wheel loader which has beendisclosed in Patent Literature 1. The wheel loader is provided withwheels, a vehicle body frame with an operator's cab, a working device,etc. The working device is provided with a lift arm which moves in anup/down direction, and a bucket which is attached to a distal end of thelift arm.

As this type of wheel loader, there is a wheel loader having an HST typedriving system. The HST type driving system is provided with an HST pumpand an HST motor which form a closed circuit, a working machine pumpwhich discharges pressure oil for driving the working device, and adriving wheel system which operates in response to an output from theHST motor.

CITATION LIST PATENT LITERATURE

Patent Literature 1: JP-A-2008-223899

SUMMARY OF INVENTION Technical Problem

In order to achieve an energy saving effect, it can be considered that apower mode and an eco mode are set for control of the HST pump and theHST motor in the aforementioned wheel loader having the HST type drivingsystem. The power mode supports heavy-load excavation. In the eco modeattaching importance to a fuel consumption reduction effect, enginespeed is suppressed to be lower than that in the power mode.

However, it can be considered that the wheel loader which has beenconfigured thus to have the eco mode has the following disadvantage.That is, the working machine pump is also directly connected to theengine and the HST pump. The discharge flow rate of the working machinepump is determined in accordance with rotation speed of an input shaftdirectly connected to the engine. Accordingly, when soil which has been,for example, held by a bucket of the working device is lifted up by thelift arm in the eco mode, operation speed of the working device maybecome slow to thereby lower working efficiency.

FIG. 8 is a graph showing input torque characteristics of the HST pumprelative to the engine speed, which have been considered from theaforementioned background-art technique. In FIG. 8, the reference sign32 designates a power mode characteristic; 31, an eco modecharacteristic; 29, an engine torque characteristic; and 30, an enginetorque characteristic which is obtained by subtracting input torque ofthe working machine pump during driving of the working device from theengine torque characteristic 29. The engine torque characteristic 30expresses engine torque which can be consumed by the HST pump. Assumethat traveling operation is performed while the working device isdriven. In this case, in the power mode, the engine is driven at amatching point B and engine speed N(B) corresponds to higher rotationspeed. On the other hand, in the eco mode, the engine is driven at amatching point A at which the engine speed is lower than that at thematching point B due to a larger increase rate of the input torque ofthe HST pump with respect to the increase of the engine speed.Therefore, rotation speed N(A) corresponds to lower engine speed. Thus,the speed of the working device becomes slower.

The invention has been accomplished in consideration of theaforementioned real circumstances in the background-art technique. It isan object of the invention to provide a wheel loader which has an HSTtype driving system and which can improve working efficiency in an ecomode in the case where a power mode and the eco mode have been set inthe wheel loader.

Solution to Problem

In order to achieve the object, the invention provides a wheel loaderincluding: a vehicle body frame; wheels; a working device which isattached to the vehicle body frame and which has a lift arm capable ofbeing rotated in an up/down direction; an engine which is attached tothe vehicle body frame; an HST traveling device in which a variabledisplacement type HST pump driven by the engine and an HST motor as adriving source for driving the wheels are connected to each other in aclosed circuit, and which has an HST pump control portion controllinginput torque of the HST pump; and a working machine pump which is drivenby the engine to discharge pressure oil for operating the workingdevice; wherein: the wheel loader further includes: a work modeselecting device which selects one from a power mode and an eco mode,the power mode serving as a work mode when the workload is a heavy load,the eco mode serving as a work mode when the workload is a light load; adetecting device which detects lifting operation of the lift arm of theworking device; and a control device which makes control so that theinput torque of the HST pump can be controlled in accordance with apreset eco mode characteristic by the pump control portion when the ecomode is selected by the work mode selecting device, and the input torqueof the HST pump can be controlled in accordance with a preset power modecharacteristic by the pump control portion when the power mode isselected by the work mode selecting device, but the input torquecharacteristic of the HST pump can be controlled in accordance with alifting operation characteristic in place of the eco mode characteristicwhen the lifting operation of the lift arm is detected by the detectingdevice after the eco mode has been selected.

The invention also provides a wheel loader having the aforementionedconfiguration, wherein: the control device has a storage portion whichstores an eco mode characteristic line, a power mode characteristicline, and a lifting operation characteristic line; each of the eco modecharacteristic line, the power mode characteristic line and the liftingoperation characteristic line includes a characteristic line expressinga relation between engine speed and the input torque of the HST pump;and the lifting operation characteristic line is set as a characteristicin which a matching point as an intersection point of the liftingoperation characteristic line with a working device operating enginetorque characteristic line obtained by subtracting torque of the workingmachine pump from torque of the engine is provided between an eco modematching point as an intersection point between the eco modecharacteristic line and the working device operating engine torquecharacteristic line and a power mode matching point as an intersectionpoint between the power mode characteristic line and the working deviceoperating engine torque characteristic line.

The invention also provides a wheel loader having the aforementionedconfiguration, wherein: the lifting operation characteristic line isprovided to diverge from the middle of the eco mode characteristic line.

The invention also provides a wheel loader having the aforementionedconfiguration, including: a multistage transmission which is connectedto the HST motor and which has a plurality of speed stages including ahigh speed stage and a low speed stage; a speed stage detecting devicewhich detects that the multistage transmission has been changed over tothe low speed stage; and a forward movement detecting sensor whichdetects that the wheel loader is in a state of forward movement;wherein: the HST motor includes a variable displacement type hydraulicmotor; the HST traveling device has an HST motor control portion whichcontrols tilting of the HST motor; and when it is detected by the speedstage detection device that the multistage transmission has been changedover to the low speed stage and it is detected by the forward movementdetecting sensor that the wheel loader is in a state of forwardmovement, the control device makes control so that minimum tilting ofthe HST motor can be set as minimum tilting larger than minimum tiltingin the eco mode by the HST motor control portion.

Advantageous Effects of Invention

According to the invention, when the lifting operation of the lift armof the working device is performed in the eco mode in the case where thepower mode and the eco mode has been set in the wheel loader having theHST type driving system, the HST pump is controlled in accordance withthe lifting operation characteristic line so that the engine speed canbe higher than that in the eco mode. Thus, according to the invention,it is possible to increase operation speed of the lifting operation ofthe lift arm of the working device so that it is possible to improveworking efficiency more greatly than in the background art. In addition,according to the invention, the lifting operation characteristic line isset to diverge from the eco mode characteristic line. Accordingly, it ispossible to carry out the lifting operation of the lift arm in the ecomode while reducing an operator's feeling of difference from a feelingof operation in the eco mode.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] A side view showing a first embodiment of a wheel loaderaccording to the invention.

[FIG. 2] An electric and hydraulic circuit diagram provided in the firstembodiment.

[FIG. 3] A block diagram showing a control system provided in the firstembodiment.

[FIG. 4] A flow chart showing a processing procedure of a vehicle bodycontroller provided in the first embodiment.

[FIG. 5] A graph showing characteristics obtained in the firstembodiment.

[FIG. 6] A block diagram showing a control system provided in a secondembodiment of the invention.

[FIG. 7] A flow chart showing a processing procedure of a vehicle bodycontroller provided in the second embodiment.

[FIG. 8] A graph showing characteristics considered from thebackground-art technique.

DESCRIPTION OF EMBODIMENTS

Embodiments of a wheel loader according to the invention will bedescribed below based on the drawings.

First Embodiment

FIG. 1 is a side view showing a first embodiment of a wheel loaderaccording to the invention. As shown in FIG. 1, the wheel loaderaccording to the first embodiment is provided with a vehicle body frame1, an operator's cab 2, wheels, i.e. front wheels 9 and rear wheels 10,and a working device 3. The working device 3 is attached to the vehiclebody frame 1. The working device 3 includes a lift arm 4, a liftcylinder 6, a bucket 5, a bucket cylinder 7, and a bellcrank 8. The liftarm 4 can be rotated in an up/down direction. The lift cylinder 6 drivesthe lift arm 4. The bucket 5 is attached to a distal end of the lift arm4 so that the bucket 5 can be loaded with soil. The bucket cylinder 7rotates the bucket 5 in the up/down direction. The bellcrank 8 forms alink mechanism between the bucket 5 and the bucket cylinder 7.

FIG. 2 is an electric and hydraulic circuit diagram provided in thefirst embodiment.

As shown in FIG. 2, the first embodiment is provided with an engine 17,a hydraulic closed circuit, and a working machine pump 13. The engine 17is attached to the vehicle body frame 1. The hydraulic closed circuitincludes a variable displacement type HST pump 11 which is driven by theengine 17, and an HST motor 14 which is driven by pressure oildischarged from the HST pump 11. The working machine pump 13 is drivenby the engine 17 to discharge pressure oil for operating the workingdevice 3. Further, the first embodiment has an HST charge pump 12 and adriving wheel system 24. The HST charge pump 12 discharges pressure oilfor controlling the HST pump 11. The driving wheel system 24 transmitsdriving force generated by the HST motor 14 to the front wheels 9 andthe rear wheels 10. The pressure oil discharged from the working machinepump 13 is delivered to the lift cylinder 6 serving as the workingdevice 3 through a control valve 35.

The first embodiment is also provided with a detecting portion, a workmode selecting portion 22 and an engine speed sensor 25. The detectingportion detects lifting operation of the lift arm 4 of the workingdevice 3. For example, the detecting portion is a working machinepressure detecting portion 23 which detects pressure of a conduit makingcommunication between the control valve 35 and a bottom chamber of thelift cylinder 6. The work mode selecting portion 22 selects one from apower mode and an eco mode. The power mode serves as a work mode whenthe workload is a heavy load. The eco mode serves as a work mode whenthe workload is a light load. The engine speed sensor 25 detects realrotation speed of the engine 17. The first embodiment is furtherprovided with a control device, i.e. a controller 18, to which pieces ofinformation are inputted from the working machine pressure detectingportion 23, the work mode selecting portion 22 and the engine speedsensor 25. Information outputted from the controller 18 is sent to anHST pump control portion 15 and an HST motor control portion 16. The HSTpump control portion 15 controls tilting (pump input torque) of the HSTpump 11 in accordance with a command from the controller 18. The HSTmotor control portion 16 controls tilting (motor output torque) of theHST motor 14 in accordance with a command from the controller 18.

Incidentally, the controller 18 controls the HST pump control portion 15so as to increase the pump tilting (pump input torque) in accordancewith the increase of the engine speed. In addition, the controller 18controls the HST motor control portion 16 so as to increase the motortilting (motor output torque) more toward maximum tilting as dischargepressure of the HST pump (driving pressure of the HST motor 15) ishigher and so as to decrease the motor tilting more toward minimumtilting as the discharge pressure of the HST pump is lower.

Traveling torque increases as the motor tilting is larger. Travellingspeed increases as the motor tilting is smaller. Thus, the travellingspeed can reach the highest speed at the minimum tilting. Thus,low-speed high-torque traveling and high-speed low-torque traveling areachieved.

FIG. 3 is a block diagram showing a control system provided in the firstembodiment. FIG. 4 is a flow chart showing a processing procedure of thevehicle body controller provided in the first embodiment. FIG. 5 is agraph showing characteristics obtained by the first embodiment.

The controller 18 shown in FIG. 3 has a storage portion 28 (see FIG. 3)which stores the relation of the input torque of the HST pump to theengine speed as a map as shown in FIG. 5. An eco mode characteristicline 31, a power mode characteristic line 32, a matching point A, amatching point B, and a lifting operation characteristic line 34 arestored in advance in the map. The eco mode characteristic line 31expresses the relation between the eco mode engine speed which is usedwhen the eco mode is selected by the work mode selecting portion 22, andthe input torque of the HST pump 11. The power mode characteristic line32 expresses the relation between the power mode engine speed which isused when the power mode is selected, and the input torque of the HSTpump. The matching point A is located on a working device operatingengine torque characteristic line 30 which is obtained by subtractingthe torque of the working machine pump 13 from the torque of the engine17 (a characteristic line 29). The matching point A is an intersectionpoint between the eco mode characteristic line 31 and the working deviceoperating engine torque characteristic line 30. The matching point B isan intersection point between the power mode characteristic line 32 andthe working device operating engine torque characteristic line 30. Thelifting operation characteristic line 34 has a matching point C which isan intersection point with the working device operating engine torquecharacteristic line 30 and between the matching point A and the matchingpoint B. The lifting operation characteristic line 34 is set to divergefrom the eco mode characteristic line 31 and expresses the relationbetween the engine speed during the lifting operation of the lift arm 4and the input torque of the HST pump.

The input torque of the HST pump during operation of the working devicematches with an intersection point on the working device operatingengine torque characteristic line 30. The engine 17 is operated at therotation speed at the intersection point. The eco mode characteristicline 31 is set in such a manner that the input torque of the HST pumpincreases at a larger increase rate relative to the increase of theengine speed. The engine speed at the matching point A corresponds tolower rotation speed N(A). Thus, the engine is operated at lowerrotation speed so that fuel consumption can be improved. The power modecharacteristic line 32 is set in such a manner that the input torque ofthe HST pump increases more gently relatively to the increase of theengine speed than in the eco mode characteristic line 31. Engine speedN(B) at the matching point B corresponds to a higher value than theengine speed N(A) at the matching point A. Therefore, the engine can beoperated at higher rotation speed to increase the discharge flow rate ofthe working machine pump 13 to thereby increase the driving speed of thelift arm 4 etc. of the working device 3. Thus, it is possible to improveworkability. The lifting operation characteristic line 34 diverges fromthe middle of the eco mode characteristic line 31. The lifting operationcharacteristic line 34 is set in such a manner that, up to thedivergence point, the input torque of the HST pump increases at a largerincrease rate relative to the increase of the engine speed in the samemanner as in the eco mode characteristic line 31, but beyond thedivergence point, the input torque of the HST pump increases gentlyrelatively to the increase of the engine speed, for example,substantially at the same increase rate as in the power modecharacteristic line 32. Engine speed N(C) at the matching point C is avalue larger than the engine speed N (A) but smaller than the enginespeed N(B). The characteristic of the engine speed N(C) is set so thatthe engine speed N(C) can be a value close to the engine speed N(B).

In addition, as shown in FIG. 3, the controller 18 is provided with adetermination portion 26, a storage portion 28, and a control portion27. The determination portion 26 determines whether the liftingoperation of the lift arm 4 of the working device 3 has been detected ornot by the working machine pressure detecting portion 23 in thecondition that the eco mode has been selected by the work mode selectingportion 22. The characteristics shown in FIG. 5 are stored in thestorage portion 28. The control portion 27 controls the HST pump 11 inaccordance with the lifting operation characteristic line 34 in place ofthe eco mode characteristic line 31 when it is determined by thedetermination portion 26 that the lifting operation of the lift arm 4has been detected.

As shown in FIG. 4, first, the determination portion 26 of thecontroller 18 determines whether the eco mode has been selected as thework mode or not (step S1). When the eco mode has not been selected,control of the HST pump 11 is made in accordance with the power modecharacteristic line 32 shown in FIG. 5 (step S2). When pressure isdetected by the working machine pressure detecting portion 23 in thecase where the eco mode has been selected, determination is made as towhether the lift arm 4 has been lifted or not (step S3). When the setworking machine pressure is not detected, determination is made that thelift arm 4 has not been lifted yet so that control of the HST pump 11 ismade in accordance with the eco mode characteristic line 31 shown inFIG. 5 (step S4). When the set working machine pressure is detected,determination is made that the lift arm 4 has been lifted so thatcontrol of the HST pump is made in accordance with the lifting operationcharacteristic line 34 shown in FIG. 5 (step S5).

Incidentally, in FIG. 5, the reference sign 29 designates an engineoutput torque characteristic line corresponding to torque obtained asthe sum of the input torque of the HST pump and the input torque of theworking machine pump. As described above, the working device operatingengine torque characteristic line 30 is a torque characteristic linerelevant to the engine 17 and corresponding to torque obtained bysubtracting the input torque of the working machine pump from the outputtorque of the engine. The input torque of the HST pump duringacceleration from a stop state of the vehicle body is expressed by theeco mode characteristic line 31, the power mode characteristic line 32and the lifting operation characteristic line 34 in FIG. 5. In the powermode, the engine speed N(B) corresponds to higher rotation speed asindicated at the matching point B. On the other hand, in the eco mode,the rotation speed N(A) corresponds to lower engine speed as indicatedat the matching point A, and the discharge flow rate of the workingmachine pump 13 decreases accordingly. However, in the lifting operationcharacteristic line 34, since the engine speed N(C) as indicated at thematching point C can be set as rotation speed higher than the enginespeed N(A), the discharge flow rate of the working machine pump 13 closeto that in the power mode can be obtained in spite of the eco mode.

According to the first embodiment configured thus, when the liftingoperation of the lift arm 4 of the working device 3 in the wheel loaderhaving the HST type driving system has been performed in the eco mode,the HST pump 11 is controlled in accordance with the lifting operationcharacteristic line 34 stored in the storage portion 28 of thecontroller 18 so that the engine speed can be increased to be higherthan that in the eco mode. Such lifting operation of the lift arm 4 iscarried out when soil held by the bucket 5 is loaded into a truck etc.or released to a mound of sediment. In this manner, according to thefirst embodiment, it is possible to increase the operation speed of thelifting operation of the working device 3 so that it is possible toimprove working efficiency.

In addition, the lift operation characteristic line 34 is set to divergefrom the eco mode characteristic line 31 in the first embodiment.Accordingly, it is possible to carry out the lifting operation of thelift arm 4 in the eco mode while reducing an operator's feeling ofdifference from a feeling of operation in the eco mode.

Second Embodiment

FIG. 6 is a block diagram showing a control system provided in a secondembodiment of the invention. FIG. 7 is a flow chart showing a processingprocedure of a vehicle body controller provided in the secondembodiment. The fundamental configuration of the second embodiment isequivalent to that of the first embodiment. Only different parts will bedescribed below.

The second embodiment is provided with a not-shown multistagetransmission, a speed stage detecting portion 20, and a forward movementdetecting sensor 21. The multistage transmission is connected to an HSTmotor 14 and is formed as a constituent part of a driving wheel system24. The multistage transmission changes rotation of the HST motor 14 toone of a high speed stage and a low speed stage so as to change thespeed. The speed stage detecting portion 20 detects that the multistagetransmission has been changed over to the low speed stage as shown inFIG. 6. The forward movement detecting sensor 21 detects that thevehicle body of the wheel loader is in a state of forward movement.

In addition to the determination made in the first embodiment, adetermination portion 26 of a controller 18 is configured to alsodetermine whether or not it has been detected by the speed stagedetecting portion 20 that the multistage transmission has been changedover to the slow speed stage and it has been detected by the forwardmovement detecting sensor 21 that the wheel loader is in the state offorward movement. A control portion 27 is configured to also output acontrol signal to an HST motor control portion 16.

In the second embodiment, as shown in the flow chart of FIG. 7, whenpressure is detected by a working machine pressure detecting portion 23so that determination is made that a lift arm 4 has been lifted in astep S3, control of an HST pump 11 is made in accordance with a liftingoperation characteristic line 34 in a step S5. Moreover, when it isdetermined by the determination portion 26 of the controller 18 that themultistage transmission has been changed over to the low speed stage andthe wheel loader is in the state of forward movement (step S6), thecontrol portion 27 of the controller 18 outputs a control signal to theHST motor control portion 15 to make control so that minimum tilting ofthe HST motor 14 can be set as minimum tilting larger than minimumtilting in an eco mode (step S8). When the condition is not consistentwith any of the low speed stage and the state of forward movement, thecontrol portion 27 controls the HST motor control portion 15 to keep theminimum tilting of the HST motor 14 at the same minimum titling as thatin the eco mode (step S7).

According to the second embodiment, not only is it possible to obtain anequivalent effect to that in the first embodiment but it is alsopossible to reduce the vehicle speed to be lower than that in the ecomode in the background art when the speed of the vehicle body isaccelerated from a stop state or a very slow speed region during liftingoperation of the lift arm 4 of the working device 3, i.e. when soil heldby a bucket 5 is loaded into a truck etc. or released to a mound ofsediment.

Here, operation speed of the working device 3 and traveling speed in apower mode are set to be balanced with each other in consideration ofworkability and operability in the wheel loader according to thebackground-art technique. Therefore, there is a fear that the balancebetween the operation speed of the lift arm 4 of the working device 3and the vehicle speed in the eco mode may be poor to lower workingefficiency. That is, since the vehicle speed is higher relatively to theoperation speed of the lift arm 4 of the working device 3 in the ecomode in the wheel loader according to the background-art technique, thetraveling distance tends to be longer, and further, there arises adifference in operability between the power mode and the eco mode.Therefore, when equivalent work to loading work etc. performed in thepower mode is intended to be performed in the eco mode, the travelingdistance required for the work in the eco mode becomes longer than thatin the power mode. Accordingly, it is difficult to do the work in anarrow work site.

According to the second embodiment, the minimum tilting of the HST motor14 is set as the larger minimum tilting as described above so that thevehicle speed can be reduced when soil held by the bucket 5 is loadedinto a truck etc . or released to a mound of sediment. Accordingly, itis possible to improve the balance between the operation speed of thelift arm 4 of the working device 3 and the vehicle speed so that it ispossible to increase the working efficiency. In addition, when the samework such as work for loading soil held by the bucket 5 into a trucketc. or work for releasing soil to a mound of sediment is performed, itis possible to make the traveling distance substantially equal betweenthe power mode and the eco mode.

REFERENCE SIGNS LIST

-   1 vehicle body frame-   3 working device-   4 lift arm-   5 bucket-   6 lift cylinder-   7 bucket cylinder-   8 bellcrank-   11 HST pump-   12 HST charge pump-   13 working machine pump-   14 HST motor-   15 HST pump control portion-   16 HST motor control portion-   17 engine-   18 controller (control device)-   20 speed stage detecting portion (speed stage detecting device)-   21 forward movement detecting sensor-   22 work mode selecting portion (work mode selecting device)-   23 working machine pressure detecting portion (detecting device)-   24 driving wheel system-   25 engine speed sensor-   26 determination portion-   27 control portion-   28 storage portion-   29 engine torque characteristic line-   30 working device operating engine torque characteristic line-   31 eco mode characteristic line-   32 power mode characteristic line-   34 lifting operation characteristic line

1. A wheel loader comprising: a vehicle body frame (11); wheels (9, 10);a working device (3) which is attached to the vehicle body frame (10)and which has a lift arm (4) capable of being rotated in an up/downdirection; an engine (17) which is attached to the vehicle body frame(10); an HST traveling device in which a variable displacement type HSTpump (11) driven by the engine (17) and an HST motor (14) driving thewheels (9, 10) are connected to each other in a closed circuit, andwhich has an HST pump control portion (15) controlling input torque ofthe HST pump (11); and a working machine pump (13) which is driven bythe engine (17) to discharge pressure oil for operating the workingdevice (3); wherein: the wheel loader further comprises: a work modeselecting device (22) which selects one from a power mode and an ecomode, the power mode serving as a work mode when the workload is a heavyload, the eco mode serving as a work mode when the workload is a lightload; a detecting device (23) which detects lifting operation of thelift arm (4) of the working device (3); and a control device (18) whichmakes control so that the input torque of the HST pump (11) can becontrolled in accordance with a preset eco mode characteristic by theHST pump control portion (15) when the eco mode is selected by the workmode selecting device (22), and the input torque of the HST pump (11)can be controlled in accordance with a preset power mode characteristicby the HST pump control portion (15) when the power mode is selected bythe work mode selecting device (22), but the input torque characteristicof the HST pump (11) can be controlled in accordance with a liftingoperation characteristic in place of the eco mode characteristic whenthe lifting operation of the lift arm (4) is detected by the detectingdevice (23) after the eco mode has been selected.
 2. A wheel loaderaccording to claim 1, wherein: the control device (18) has a storageportion (28) which stores an eco mode characteristic line (31), a powermode characteristic line (32), and a lifting operation characteristicline (34); each of the eco mode characteristic line (31), the power modecharacteristic line (32) and the lifting operation characteristic line(34) includes a characteristic line expressing a relation between enginespeed and the input torque of the HST pump (11); and the liftingoperation characteristic line (34) is set as a characteristic in which amatching point as an intersection point of the lifting operationcharacteristic line (34) with a working device operating engine torquecharacteristic line (30) obtained by subtracting torque of the workingmachine pump (13) from torque of the engine (17) is provided between amatching point as an intersection point between the eco modecharacteristic line (31) and the working device operating engine torquecharacteristic line (30) and a matching point as an intersection pointbetween the power mode characteristic line (32) and the working deviceoperating engine torque characteristic line (30).
 3. A wheel loaderaccording to claim 1, further comprising: a multistage transmissionwhich is connected to the HST motor (14) and which has a plurality ofspeed stages including a high speed stage and a low speed stage; a speedstage detecting device (20) which detects that the multistagetransmission has been changed over to the low speed stage; and a forwardmovement detecting sensor (21) which detects that the wheel loader is ina state of forward movement; wherein: the HST motor (14) includes avariable displacement type hydraulic motor; the HST traveling device hasan HST motor control portion (16) which controls tilting of the HSTmotor (14); and when it is detected by the speed stage detection device(20) that the multistage transmission has been changed over to the lowspeed stage and it is detected by the forward movement detecting sensor(21) that the wheel loader is in a state of forward movement, thecontrol device (18) makes control so that minimum tilting of the HSTmotor (14) can be set as minimum tilting larger than minimum tilting inthe eco mode by the HST motor control portion (16).
 4. A wheel loaderaccording to claim 1, wherein: the lifting operation characteristic line(34) is provided to diverge from the middle of the eco modecharacteristic line (31).
 5. A wheel loader according to claim 2,wherein: the lifting operation characteristic line (34) is provided todiverge from the middle of the eco mode characteristic line (31).
 6. Awheel loader according to claim 2, further comprising: a multistagetransmission which is connected to the HST motor (14) and which has aplurality of speed stages including a high speed stage and a low speedstage; a speed stage detecting device (20) which detects that themultistage transmission has been changed over to the low speed stage;and a forward movement detecting sensor (21) which detects that thewheel loader is in a state of forward movement; wherein: the HST motor(14) includes a variable displacement type hydraulic motor; the HSTtraveling device has an HST motor control portion (16) which controlstilting of the HST motor (14); and when it is detected by the speedstage detection device (20) that the multistage transmission has beenchanged over to the low speed stage and it is detected by the forwardmovement detecting sensor (21) that the wheel loader is in a state offorward movement, the control device (18) makes control so that minimumtilting of the HST motor (14) can be set as minimum tilting larger thanminimum tilting in the eco mode by the HST motor control portion (16).7. A wheel loader according to claim 3, wherein: the lifting operationcharacteristic line (34) is provided to diverge from the middle of theeco mode characteristic line (31).
 8. A wheel loader according to claim6, wherein: the lifting operation characteristic line (34) is providedto diverge from the middle of the eco mode characteristic line (31).